Combustion equipment for gas-turbine engines with anticarbon wall portion



April 10, 1956 F. M. JOHNSON COMBUSTION EQUIPMENT FOR GAS-TURBINEENGINES WITH ANTICARBON WALL PORTION 5 Sheets-Sheet 1 Filed April 10,1950 INYENTOR FRANCIS r1 a'ouusou MM; WQHKZ I Arra/ZNEYS l/ Aprll 10,1956 JOHNSON 2,741,090

COMBUSTION EQUIPMENT FOR GAS-TURBINE ENGINES WITH ANTICARBON WALLPORTION Filed April 10, 1950 5 Sheets-Sheet 2 INVEA/TUR FRANCIS M.JOHNSON April 10, 1956 F. M. JOHNSON 2,741,090

COMBUSTION EQUIPMENT FOR TU INE ENGINES WITH ANTICARBON w PO 0N FiledApril 10, 1950 v 3 Sheets-Sheet 3 mm m F. MJ OHNSON l; l/w w awn UnitedStates Patent D COMBUSTION EQUIPMENT FOR "GAS-TURBHQE ENGINES WITHAYTICARBQN WALL PORTEQN Francis Murray Johnson, Sireatham, London,England, assignor to Rolls-Royce Limited, Derby, England, aBritishcompany Application April 19, 1951}, Serial No. 154365 Claimspriority, applicationGrcat Britain dune :30, U4)

8 Claims. {CL 69- 3165) This invention relates tocombustion equipmentfor gasturbine engines. "It-is concernedwith combustion equipment of thekind comprising afiame tube accommodated Within an air casing, so as toprovide a passage between the outer-wall of the flametube and theair-casing through which air passes before being introduced into theflame tube through suitable apertures or entry ducts, andwherein primaryair is introduced at the inlet end of the flame tube. In combustionequipment of this kind there are at least two distinct supplies of airinto the interior of the flame tube, referred to as primary air, withwhichcombustion of the fuel is initiated, and mixing air, which isintroduced mainly to-dilute the combustion gases and to coolthern. Themixing airmay also assist thecomp'l'e- 'tion of combustion.

It has hitherto been the practice in combustion equipment of the kindspecified, to provide fuel injection'means at the inlet end of the flametube to introduce a spray of atomized'liquid fuel into the flame tubeand to introduce primary air into the flame tube through-a perforatedbaffle, or swirling device which surrounds the fuel injection means.Certain such arrangements have included a 'wall portion of the'flametube at'its in'let-endwhich isdivergent in the direction of the flow-ofair 'therethroug'h.

It has been found in practice that withzsuch lcnownarrangements there-is a tendency for the formation of a carbon deposit on the perforatedbaflle or swirl device through which the primary air-is introducedand/oron-the divergent wall portion, which deposit adverselyait'ectstl'ic metering-of the primary air. into the combustion chamber.As a result, deterioration of combustion efliciency 'has *occu'rred,adversely 'afiecting the operation'o'f the engine.

The primary-object 'of' the present invention -'is to reduce or obviatethe tendency forcar'bon to be'deposited on 'the flame tube parts in theregion of introduction of=prirnary air, whereby such undesirabledeterioration of combustion e'fiiciency is avoided.

According to'the present invention, in cornbustion equipment of the kindspecified for gas-t-urbine engines, the flame tube has, at its inletend, a wall portion which is divergent in the direction of the flow ofair'through the flame tube, which wall portion constitutes part of theboundary surface of the space Within the flame tube, and has supportedadjacent to the wall portion an annular-part of divergent substantially'frusto-conicalflform located'so as to constitute with the wall portionan annular channel through which a major-parrot the flow of primary airis introduced into the flame tube, the primary air emerging from thechannel alongthe inner surface of the wall portion.

Adoption of the invention provides that the main flow ofprimary-air intothe flame tube takes place along the surface oftheldivergentwall'portion, to sweeppthis surface Preferably the cross-sectional areaof the channel in the 2,741,090 Patented Apr. '10, 1-956 direction ofairflow therethroug'h-is convergent toproduee an acceleration of flowand thus to increase the scouring action of the primary air flowalong't-he surface of the divergent wall portion.

The invention is applicable to one type of combustion equipment of thekind specified in which there-are a plurality of flame tubes of tubularform accommodated each within a separate tubular air casing, so that thegap 'between the wallof-the flame tube and the air "casing is ofannularsection. 7

The invention is also applicableto'another type of combustioncquipmentof the kindspecified in whichthe flame tubes are of tubular form and areaccommodated "within an air casing of annular construction, so thatap'lurality or flame tubes are accommodated in asingle annular aircasing.

A third type of combustion equipment of the kind-specitied to which theinvention is applicable is that in which the flame tube is itself ofannular form, accommodated within an annular air casing.

in applying the present inventionto combustion equipof the first andsecond types mentioned, one ,preferred construction provides a divergentWall portion-and annular part which are both of divergent tubular form,the divergent wall portion being connected to the inlet end 0t themain-wall portion of the flame tube, and the annular' part beingsupported internally of the divergent-wall portion to provide an annularchannel for the passage of primary air into the flame tube. In such anarrangement uelinjection means may be provided concentrically-within theannular part to introduce atomized :or'vaporized fuel into-theflameatube at-its'irilet end.

In applying the invention to the third type of combustion equipmentmentioned oneprefferred constructionprovides a first divergent wallportion 'whic'h'is attached 'to theinlet end of the main portion of anouter defining Wail of the annular-flame tube, Whilea second wallportionfis attached to the inlet end of the mairrportion of the innerdefining'wall of-the annular-flame tube, the twowall'portions togetherdefining a space between the inner and'out er walls 'ofthefiarnetube'which is divergent in the direction of the flow of airthrough the fiametube; likewise an annular part ;is associated'with eachof the wall portions mentioned, so that inner and outer annular channelsare constituted for the passage 'o'f prirnary air' into 'theiinterinr ofthe flame tube. With such .an arrangement a series-of fuel injectionmeans are conveniently located circumferentially in'the annulus "between'the 'two annular parts to introduce fuel in'atomized or vaporized formtoiflieicombustion chamber.

According to a feature of this invention a subsidiary flow of primaryair may be introduced into the flame tube in the region :of thetransverse plane through the flame "tube approximately containing thedownstream and of the annular ringpart or parts. Thus in the case of'thefirstand second types .of combustion equipmentmentionedsuchsubs'idiaryflow mayibe introduced through an annular areabetween the fuel injectionmeans and the downstream end of the annularpart, While in "the case of the third type of combustioneouiprnentmentioned the subsidiary flow *may be introduced through anannular area between the .two annular. parts. Preferably "suchsubsidiary 'air'is "supplied to the interior of the'flametubewith adegree of swirl given it by swirl vanes which, due to the tangentialvelocity component of the subsidiary flow of primary air, areefliciently scoured to reduce the tendency for carbon to depositthereon.

Aifurther feature of'theinvention provides for a further-.subsidiary:flow .of primary air between :the 1 fuel injectionmeans-and :the flame tube at :itSinlet end.

In arrangements of combustion equipment according to the presentinvention the supply of primary air to the inlet end of the frame tubeis preferably effected from the engine compressor through a divergententry duct, which may be formed integrally with the flame tube or whichof air in the delivery duct so that some of it passes into the'divergentduct while the remainder passes externally thereof and thence into thespace between the flame tube and air casing, whence it passes into theinterior of the flame tube as mixing air. The divergent entry duct mayinclude an internal duct-defining liner connecting at its downstreamend'with the inlet end of the divergent wall portion of the flame tube.

Fig. 3 shows a modified form of gas turbine engine to' which theinvention is applicable,

Fig. 4 shows a further modified form of gas turbine engine in accordancewith the invention, and Figure 5 is a perspective view from within thecombustion space looking on the fuel injection device.

The gas turbine engine of Fig. 1 comprises a compressor deliveringcompressed air to combustion equipment 11, from which the products ofcombustion pass through a turbine 12 which drives the compressor 10, andthence through a jet pipe 13 having a propelling nozzle 14, toatmosphere. The engine is suitable for aircraft jet propulsion.

The combustion equipment 11 comprises a plurality of substantiallytubular flame tubes within substantially tub ular air casings. One suchair casing and flame tube is is of generally cylindrical form, the axisof which lies on the axis of the flame tube. The fuel injection meansmay be as described in U. S. Patent No. 2,700,416 which issued onJanuary 25, 195 5 where provision is made to prevent or reduce thetendency to carbon formation on the I orifice part or parts of the fuelinjector.

shown in section in Fig. 2, the arrangement comprising an entryexpansion chamber portion 15 which is connected with the delivery of theengine compressor 10 and is of divergent substantially circularcross-section. The expansion chamber 15 is connected by a bolted flangejoint 16 with a tubular main air casing part 17 which in turn isconnected at its outlet end with a nozzle entry assembly of the turbine12. Internally of the air casing 17 there is accommodated a generallytubular flame tube 18; The flame tube 18 is spaced from the Wall of theinto the expansion chamber 15 and provides a passage for the flow ofmixing air into the flame tube. 7

Within the expansion chamber 15 is mounted aduct air casing 17 and intoa primary air flow which passes through the divergent entry duct 20ainto the interior of the flame tube '18 at its entry end. The divergententry duct part 20 is also formed at its downstream end 20c with aspigot flange 21 which serves to support the flame tube 18, so that theentry duct 20 is in effect an extension of the flame tube 18 into theexpansion chamber 15.-

Fuel injection means 22 is supported on the axis of the flame tube inthe plane of the exit end of the divergent entry ductpart 20, beingconveniently carried on a boss 23 by a number of legs 24 (one only ofwhich is shown 1 in the drawing) cast integrally with the entry ductpart air casing 17 to form an annular duct 19 which extends.

part-20, defining adivergent entry duct 20a, the smaller The inlet endof the flame tube is of double skin formation, the outer skin 25 ofwhich provides the socket for the spigot 21 on the divergent entry ductpart 20, and the inner skin 26 of which is spaced inwardly of thedivergent entry duct part 20, to constitute'a divergent annular wallportion of the flame tube. This portion spigots at its inlet end 26:: inan annular socket 27 on a sheet-metal liner 28 within the divergententry duct 20a. At its outer end 26b the divergent wall portion 26connccts with a substantially cylindrical main portion of the flame tube18. Within the divergent wall portion 26 an annular ring 29 ofdivergent, substantially frustoconical form is provided, which ring isof less axial length and less maximum diameter than the divergent wallportion 26 of the flame tube. The ring 29 is located so as to provide,with the divergent wall portion 26, an annular channel 39 whichconverges from its inlet end 30a, which end lies substantially in theplane of the exit end Ziic of the divergent entry duct 20a to receiveair therefrom, to its outlet end 39b which lies adjacent the divergentface of the inner wall 26. The ring 29 is spaced from the inner skin 26by means of tubular spacer members 31, and is supported by bolts 32which conveniently pass through the spacer members 31.

tially without swirl, in a direction parallel to the surface of thedivergent wall portion 26 so as to scour this surface.

A sleeve 33 surrounding the fuel injector 22 is supported within thering 29 by a number of swirl vanes 34. The latter (see Figure 5) are soshaped and disposed relative to one another as to provide passages for asubsidiary flow of primary air which at entry are substantially axial i.e. the entry areas face upstream into the divergent .entry duct, whileat exit the passages 35 direct the air flow with a considerabletangential component of velocity into the flame tube 18. Further thepassages 35 between the vanes 34 are convergent 'so that relatively highexit velocity is obtained preventing or reducing the tendency for carbonto be deposited on the exit surfaces of the vanes 34. A further annu--takes place through the annular channel 30 defined between the divergentwall portion 26 of the flame tube and the .ring 29 associated therewith,while comparatively minor subsidiary flows of primary air take placethrough the swirl vane passages 35 and through the annular passage 36surrounding the fuel injector 22.

These flows of primary air will reduce or obviate the" tendency forcarbon to be deposited on the flame tube parts in the region ofintroduction of primary air.

Y A modified form of gas turbine engine to which the invention'isapplicable is shown in transverse cross section in Fig. 3. In thisarrangement the combustion equipment 11a comprises a plurality of flametubes 18 accommodated in a single annular air casing 117, which 20. Thefuel injection means 22 may be of any known or convenient kind, and ispreferably of the kind injecting liquid fuel as an atomized spraythrough an atomizing orifice. The fuel injection means 22 in thisembodiment to such an arrangement.

is co-axial with the compressor 10 and the turbine 12 of the engine. Itwill be appreciated that the construction according to the invention.may be readily applied Each flame tube 18 will be i identical with thoseof the embodiment already described,

as will be the divergent entry duct part 20 corresponding with eachflame tube. The annular air casing 117 comprising an inner member 117aand an outer member 117b is bolted to an annular expansion chamber ofdivergent cross sectional area in the-direction of the flow of air.

A further modified form of gas turbine engine to which the invention isapplicable is shown in transverse cross section in Eig. 4. In thisarrangement, combustion equipment 11b comprises a single annular flametube 218 accommodated in a single bar casing 217, both of which areco-axial with the compressor 16 and the turbine 12 of the engine. Theconstruction according to the invention may also be readily applied tothis arrangement, as will be appreciated. Each flame tube 218, whilebeing identical with that of the first embodiment above described inlongitudinal cross section, will extend circumferentially to form acontinuous annular duct. The inner member 217:: and the outer member217k of the annular air casing 217 will be bolted to an annularexpansion chamber of divergent cross-sectionm area in the direction ofthe flow of air. The divergent entry duct part 29 will support the inletend of the annular flame tube 218.

I claim:

1. Combustion equipment for a gas-turbine engine comprising an aircasing and a flame tube accommodated in said air casing and defining acombustion space Within said flame tube, said flame tube having animperforate inlet wall portion curved away from said combustion spaceand bounding a duct through which air flows into said flame tube, afirst part of said inlet wall portion being convex toward saidcombustion space, and a second part of said inlet wall portionimmediately downstream of said first part being frusto-conical andbounding the combustion space and being divergent with respect to saidflow of air whereby carbon formation is liable to occur on said secondpart, and a further wall portion which is adjacent said inlet wallportion, is curved away from said combustion space and .is located onthe side of said inlet wall portion adjacent said combustion space, saidfurther wall portion being at least in part convex toward saidcombustion space, said further wall portion and said inlet wall portionaffording between the inlet wall portion andithe whole length of thefurther wall portion an annular channel curved away from said combustionspace, and said second part of the inlet wall portion beingsubstantially Wholly beyond the downstream end .of said further wallportion, whereby air entering the combustion space through said channelpasses along the surface of said second part of the inlet wall portion,whereby carbon formation on said second part is substantially reduced.

2. Combustion equipment for a gas-turbine engine comprising an aircasing and a flame tube accommodated in said air casing and defining acombustion space within said flame tube, said flame tube having animperforate inlet Wall portion curved away from said combustion spaceand bounding a duct through which air flows into said flame tube, afirst part of said inlet wall portion being convex toward saidcombustion space, and a second part of said inlet wall portionimmediately downstream of said first part being frusto-conical andbounding the combustion space and being divergent with respect to saidflow of air whereby carbon formation is liable to occur on said secondpart, and a further wall portion which is adjacent said inlet wallportion is curved away from said combustion space and 'is located on theside of said inlet wall portion adjacent said combustion space, saidfurther wall portion being at least in part convex toward saidcombustion space, and said further wall portion lying nearer to saidinlet wall portion at its downstream end than at its upstream endthereby to define between the inlet wall portion and the whole length ofthe further wall portion an annular channel which is curved away fromsaid com- 6 bustion space and which converges from its inlet end to itsoutlet end, and said second part of the inlet wall portion beingsubstantially wholly beyond the downstream end .of said further wallportion, whereby air entering the combustion space through said channelpasses along the surface of said second part of the inlet wall portion,whereby carbon formation on said second part is substantially reduced.

3. Combustion equipment for a gas-turbine engine comprising a tubularair casing and a tubular flame tube accommodated in said air casing anddefining a combuslion space within the flame tube, said flame tubehaving an imperforate-inlet wall portion curved away'from saidcombustion space towards the air casing and formed substantially as .abody .of revolution bounding aduct through which air flows intovsaidflame tube, a first part of said inlet wall portion being convex towardsaid combustion space, and a second part of said inlet Wall portionimmediately downstream .of said first part being frustoconical andbounding the combustion space and being divergent with respect tosaidflow of air whereby carbon formation .is liable to occur on saidsecond part, and a further wall portion which is adjacent said inletwall portion, is curved away from said combustion space, and

is located on the side of said inlet wall portion adjacent saidcombustionspacm'said further Wall portion being at least in part convextoward said combustion space, said further wall portion and said inletwall portion affording between the inlet wall portion and the wholelength of the further wallportion an annular channel curved away fromsaid combustion space and'said second part of the inlet wall portionbeing substantially wholly beyond the downstream end .ofsaid furtherwall portion whereby air entering the combustion spacethrough saidchannel passes along the surface of saidsecond part of the inlet wallportion, wherebytcarbon formation on said second part is substantiallyreduced.

4. Combustion equipment for a gas-turbine engine comprising a tubularair casing and a tubular flame tube accommodated in said air casing anddefining a combustion space within said flame tube, said flame tubehaving an imperforate inlet :wall portion curved away from saidcombustion space toward the air casing and formed subvstantially as abody of revolution bounding a duct through which air flows intosaid'fiame tube, a first part of said wall portion being convex towardsaid combustion space,

and a second part of said wall portion immediately downstream of saidfirst-partbeing frusto-conical and bounding the combustion space andbeing divergent with repect to said fiow of air whereby carbon formationis liable to occur on said :second part, and a further wall portionwhich is adjacent said inlet wall portion, is curved away from saidcombustion space and is located on the side of said inlet wall portionadjacent said combustion space, said further wall portion being at leastin part convex toward said combustion space, and said further wallportion lying nearer to said inlet wall portion at its downstream endthan at its upstream end thereby to define between the inlet wallportion and the whole length of the further wall portion an annularchannel which is curved away from said combustion space and whichconverges from its inlet end to its outlet end, and said second part ofthe inlet wall portion being substantially wholly beyond the downstreamend of said further wall portion, whereby air entering the combustionspace through said channel passes along the surface of said second partof the inlet wallportion, whereby carbon formation on said second partis substantially reduced,

'5. Combustion equipment :for a gas-turbine engine comprising an annularair casing having an inner annular wall and an outer annular wall, and aplurality of tubular flame tubes accommodated in said air casing anddefining a combustion space within each of said flame tubes, eachof-said flame tubes having an imperforate inlet wall portion curved awayfrom said combustion space and formed part is substantially reduced.

carbon formation is liable to occur on said second part,

and a further wall portion which is adjacent said inlet wall portion iscurved away fiom said combustion space and is located on the sideof saidinlet wall portion adjacent said combustion space, said further wallportion being at least in part convex toward said combustion space, saidfurther wall portion and-said inlet wall portion aifording between theinlet wall portion and the a whole length of the further wall portion anannular channel curved away from said combustion space, and said secondpart of the inlet wall portion being substantially wholly beyond thedownstream end of said further wall portion, whereby air entering thecombustion space through said channel passes along the surface of saidsecond downstream part of the inlet wall portion, whereby carbonformation 'on said second part is substantially reduced. v j

6. Combustion equipment for a gas-turbine engine comprising an annularair casing having an inner annular wall and an outer annular wall, and aplurality of tubular flame tubes accommodated in said air casing anddefining a combustion space within each of said flame tubes, each ofsaid flame tubes having an imperforate inlet wall portion curved awayfrom said combustion space and formed substantially as a body ofrevolution bounding a duct through which air flows into i said flametube, a first part of said inlet wall portion being convex toward saidsaid combustion space, and a second part of said inlet wallportionimmediately downstream of said first part being frusto-conical andbounding the combustion space and being divergent with respect to saidflow of air whereby carbon formation is liable to occur on said wallportion adjacent said combustion space, said further 1 wall portionbeing at least in part convex toward said combustion space, and saidfurther wall portion lying nearer to said inlet wall portion at itsdownstream end than at its upstream end thereby to define between theinlet wall portion and the whole length of the further wall portion anannular channel which is curved away from said combustion space andwhich converges from its inlet end to its outlet end, and said secondpart of the inlet walllportion being substantially Wholly beyondthe'downs'trearn end of said further wall portion, whereby air enteringthe combustion space through said channel passes along the surface ofsaid second part of the inlet wall portion, whereby carbon formation onsaid second 7. Combustion equipment for a gas-turbine engine comprisingan annular air casing having an inner annular wall and an outer annularwall, and an annular flame tube accommodated in said air casing andhaving an inner annular flame tube wall and an outer annular flame tubewall spaced from the respective air casing walls and defining acombustion space between the flame tube walls, said flame tube havinganimperforate inner inlet Wall portion and an imperforate outer inlet Wallportion, each part of said inner inlet wall portion immediately downstream of said first part being frusto'conical and bounding thecombustion space and extending inwardly. from the first part towards theinner air casing wall ,whereby carbon formation is liable to occur onsaid second part, and a further inner wall portion which is, adjacentsaid inner inlet wall portion, is curved away from said combustion spaceand is located on the side ofsaid inner inlet wall portion adjacent saidcombustion space, said further inner wall portion being at least in partconvex toward said combustion space, said further inner Wall portion andsaid inner inlet wall portion aftording between the inner inlet wallportion and the whole length of the further inner wall portion a firstannular channel curved away from said combustion space, and said secondpart of the inner inlet wall portion being substantially wholly beyondthe downstream end of said further inner wall portion, whereby airentering the combustion space through said first annular channel passesalong the ,surface of said 7 second part of the inner inlet wall portionand carbon formation on said second part is substantially reduced,

'said imperforate outer inlet wall portion having aifirst part which isconvex towards the combustion space and,

a second part which is immediately downstream of said first part of theouter inlet wall portion and is frustoconical and extends outwardly fromthe first part towards the outer air casing wall whereby carbonformation is liable to occur thereon, a further outer wall portion whichis adjacent said outer inlet wall portion, is curved away from saidcombustion space and is located on the side of said outer inlet wallportion adjacent said combustion space, said further outer wall portionbeing at least in part convex toward saidcornbustion space, said furtherouter wall portion and said outer inlet wall portion afiord ing betweenthe outer inlet wall portion and the whole length of the further outerwall portion a second annular comprising an annular aircasing having aninner annular wall and an outer annular Wall, and an annular flame tubeaccommodated in said air casing and having an inner annular flame tubewall and an outer annular flame tube wall spaced from the respective aircasing walls and defining a combustion space between the flame tubewalls, said flame tube having an imperforate inner inlet wall portionand an imperforate outer inlet wall portion, each of said inlet wallportions being curved away from said combustion space towards theadjacent annular wall of the air casing and being formed substantiallyas abody of revolution, said inlet wall portions together bounding anair inlet duct through which air flows toward said combustion space, afirst part of said inner inlet wall portion being convex toward saidcombustion space, and a second part of said inner inlet wall portion,immediately downstream of said first part being frusto-conical andbounding the combustion space and extending inwardly from the first parttowards the inner air casing wall wherea by carbon formation isliable'to occur on said second part, and a furtherinner'wall'portionwhich is adjacent said inner inlet wall portion, iscurved away from said combustion space and is located on the side ofsaid inner inlet wall portion adjacent said combustion space, saidfurther inner wall portion beingat'le'ast'in part convex toward saidcombustionspace, said further innerwall' portion lying nearer to saidinner inlet wall portion at its downstream end than atits 'upstre'am'end thereby to define between the inner inlet wall portion and the wholelength of the further innerwall portion "a first annular channel curvedaway from said'combu'stion space, and said second part of the innerinlet wall portion being substantially wholly beyond the downstream endof said further inner wall portion, whereby air entering the combustionspace through said first annular channel passes along the surface ofsaid second part of the inner inlet wall portion and carbon formation onsaid second part is substantially reduced, said imperforate outer inletwall portion having a m st part which is convex towards the combustionspace and a second part which is immediately downstream of said firstpart of the outer inlet wall portion and is frusto-conical and extendsoutwardly from the first part towards the outer air casing wall wherebycarbon formation is liable to occur thereon, a further outer wallportion which is adjacent said outer inlet wall portion, is curved awayfrom said combustion space and is located on the side of said outerinlet wall portion adjacent said combustion space, said further outerwall portion being at least in part convex toward said combustion space,said further outer wall portion lying nearer to said outer inlet wallportion at its downstream end than at its upstream end thereby to definebetween the outer inlet wall portion and the whole length of the furtherouter wall portion a second annular channel curved away from saidcombustion space, and said second part of the outer inlet wall portionbeing substantially wholly beyond the downstream end of said furtherouter wall portion, whereby air entering the combustion space throughsaid second annular channel passes along the surface of said second partof the outer inlet Wall portion and carbon formation on said second partis substantially reduced.

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